The end of the road for digital radio

I have been driving an EV for a month now. No more spark ignition to suppress. No pesky electronic Diesel injectors.
So smooth and quiet a ride - I call it the MagicCarpet.
Common to most EV and Hybrid vehicle systems is a number of high power electronic inverters to drive the 100kW or so electric motors and regenerate to the storage battery. Some manufacturers such as Tesla and BMW disable the  AM band reception because of this.


I thought it would be interesting to enable the AM radio and also run the DRM digital AM tests to see if COFDM can improve reception under high noise conditions.

First step is to scan the bands with a spectrum analyzer and record the noise floor with vehicle off and then driving.

0 thru 40 MHz is where the major trouble is, +40dB of noise. There is minimal disturbance 50MHz and up, so FM, DRM+ /  DAB bands should not be an issue.











Enabling the radio for AM band is the next step. Followed some posts on the net and all is working in that area.
The reception is very good while parked up. Nearest local is 50km away and clear, big surprise that it's networked AM station some 500km away also readable here during the day. As soon as driving is started they get wound up in lots of electro-noise, some of it quite musical. The local station is part useable when driving around, but not good enough to be acceptable for owners accustomed to and in primary coverage of FM or DAB+ services. I would descibe the quality as on par with the shortwave and DAB service, both have been discontinued in this region.

I will keep the AM band enabled, it works well enough in the primary coverage contour, where there are 15 stations vs. the  3 'local' FM services available.

Today the test antenna and DRM receiver with DReaM decoder as used previously was fitted up to the car and performance tested in similar conditions to the other tests done.
While the DRM did work stationary, it was rendered unuseable while driving, with silence intervals of 2 - 3 minutes and the occasional burst of stuttery audio lasting up to 10 sec. at a time.
A re-run with AM mode transmitted showed good reception throughout the area free of serious degradation from the electric drive noise.

Final Conclusion
The reception difficulty is caused by the vehicle systems. Current developed digital radio does not overcome this, neither should it be expected to.
In - car radios should continue to tune AM and shortwave bands as it may still be relevant for the area. DRM specification radios include a range of bands less affected by this type of EV interference.

The results are specific to the BMWi series vehicles and probably their -e suffix variants. There doesnt seem to be anywhere quiet for antenna location and the body is carbon fibre / plastic therefore shielding from the electrical system is difficult.
 I have also sampled the Toyota Prius system at similar field strength AM and the degradation when in electric drive mode is present but to a lesser degree, in the order of 10dB.

It is expected the issues will be similar for all EV systems and may extend into the higher bands with some models. Lets hope RF induction charging doesnt take hold!

" It's radio, Drm, but not radio as we know it "

Digital Radio Mondiale is a broadcast radio standard designed to complement or replace legacy radio transmitters where broadcasters might require more stations, coverage area or signal quality than currently possible with existing analogue and digital radio systems.
 It uses an OFDM radio transmission scheme enabling  callsign ident, text, voice, music, data, moving & still images, in radio channel bandwidths from 2.5kHz (non-standard ham mode) thru 96kHz (DRM+ FM band digital radio). It can operate in a single frequency network (SFN) to reduce band congestion and work over HF paths – enabling continental coverage from as few as 2 or 3 transmitter sites.

I embarked on a series of experiments to test it out....

Although the mode is long established in Oceania, alongside AM on the HF broadcast bands, development of a viable consumer radio capable of reception has not yet reached the marketplace. Two practical means for hobbyists are adding converters to a traditional radio or running a SDR such as the Softrock, Elektor or FiFi kits, in each method an audio range IF signal is processed by a PC to demodulate the information.
Using some excellent open source software written for DRM, I started some real world testing beginning with converting various receivers and construction of an IQ modulator/exciter to better explore the mode's capabilities.

The main software is

DReaM (early versions include a basic DRM30 transmitter mode),
SoDiRa which has DRM+ and useful analog rx modes,
Spark a versatile transmitter program.
For narrowband DRM these programs operate anywhere within the 0-22 kHz PC soundcard range.

Assembling the rx chain using an existing radio is relatively simple, tap in at IF prior to filters then down - mix to the new souncard IF of 12 kHz – normally achieved with something like an NE602 mixer per various ccts. on the web. With availability of SDR kits, there is no need to modify a radio or build a convertor, but it will be necessary to control the reception with a keyboard and screen.
The Sony STR-VX20S I used has enough room inside for a Mini-iTX PC such as Intel Atom D525 to be installed, making it a fully functional box operated entirely with the original controls.

Audio from Sines, Portugal 15.440MHz - 12,000 miles away
https://www.dropbox.com/s/b15mubgmdgo5ttz/XRadio%20Shortwave%20Digital.ogg?dl=0

Audio from Issoudun, France 15.775MHz
https://www.dropbox.com/s/ph5mbrl40yowad6/DRM%20The%20Disco%20Palace.ogg?dl=0

For the test transmitter suite, I constructed a conventional IQ modulator using a hybrid transformer and capacitors to supply two 90 deg. split local oscillator feeds, a pair of SBL1-1 mixers, filtering and linear amplifier stages.

It is adequate for one-off testing purposes and the fine alignment is done in the PC setup. Best to use a dedicated PC for this so there are no interrupts and spurious audio tones to blow the transmitter out the window!

It soon became evident that the high crest factor of OFDM signals is a real handicap when using a regular 100 watt transmitter: the average power reaches 10 watts and saturation occurs.


 Looking for a suitable tube linear, it just happened that the first transistorised  marine coast station HF ssb transmitter from ZLW  still existed in storage. I initiated a mission to rescue it with assistance from Steve ZL2KG.






For a rating of 1kw PEP it is made up of 528 rf transistors mounted in blocks of 6, arranged in 8 PA modules, 324 of these are the finals.

Comparison results over a skywave path to Mike ZL1BTB, 250km downrange, in the 160m and 80m bands, at the same 50w carrier power levels, favoured the DRM signal signficantly over regular AM.

Mobile coverage is somewhat harder to evaluate due to the lack of any properly designed receivers in the market, AGC has an influence on the decoder performance so a mobile receiver may need to be more carefully engineered. Sony's discontinued models such as SW-7600G and SW-1 are a good reference design startpoint.

Obtaining modern radios with Shortwave has been a difficulty, however the 2010 onwards model range of JVC and Pioneer car radios includes some with SW bands 2.3 - 22 MHz, albeit with some gaps. Even the base "mech-less" model MVH-1450UB has SW band. These radios are processor based inside, so it is not possible to decode the DRM signal externally, One must wait for the manufacturers to include the available baseband decoder chips within. A most up to date place for developments is the DRMNA blogsite 

drmnainfo.blogspot.com/

Roadtrip Results 2015 update

The transmitter was run at average power of 100 Watts, with an Icom 706 receiver in the truck connected via IF converter where necessary to the appropriate software demodulators. Most tests were done with the in-vehicle audio, some shorter tests recorded audio directly in software.

Reception of 100 watt DRM30 10kHz 64QUAM transmission 10 km local route.
https://www.dropbox.com/s/87c9knk13pyrlhm/DRM%2010k%2064Q%20mobile%20reception.ogg?dl=0



Reception of 100 watt AM stereo CQUAM NRSC-1 transmission, 10km local route with SoDiRa, AGC in peak, fast mode, 7.5k baseband audio and de-emphasis added in Audacity
https://www.dropbox.com/s/z9wes9ucpawhxsm/AMAX%20test%207k5%20NRSC-1%20alonenow.ogg?dl=0


The worst part of AM broadcast is the poor receivers.
In the late '80s the AMAX standard was suggested to allow better fidelity when conditions allow but with rollback to narrowband in poor reception areas.
Ironically, most medium / high power transmitters are now supplied with CQUAM already in the modulator. For long range coverage of sparsely populated areas, this is the best choice available today.
It ain't broken, so nothing to fix. Someone needs to tell the radio makers though. Not convinced? here is a better example
AM stereo ROCKS



Reception audio tracks of Roadtrip, 100 watt DRM30 transmission then 100 watt AM transmission over the same 20 km route, 2 channel comparison, L ch = DRM, R ch = AM, start of each track approx. same part of journey, stationary at same location for last 8 mins of recording. May be easier to listen to the tracks separately.
https://www.dropbox.com/s/oq7ehsk8z22hcin/DRM%20vs%20AM%20Roadtrip.ogg?dl=0



Reception of Roadtrip, 100 watt AM stereo transmission same 20 km route.
https://www.dropbox.com/s/23spnxiu1eqr8kp/CQUAM%20roadtrip%20100W.ogg?dl=0




Reception audio tracks of Roadtrip, 100 watt P25 digital transmission then 100 watt SSB transmission over the same 20 km route, 2 channel comparison, L ch = P25, R ch = SSB, start of each track approx. same part of journey, stationary at same location for last 8 mins of recording. May be easier to listen to the tracks separately.
https://www.dropbox.com/s/0bq7d1hc7aaxouy/P25%20vs%20ssb%20Roadtrip.ogg?dl=0

Ray Of Light - nanowave aetheradio with Optomod

There are lots of ways to communicate via lightwaves and this project gets started with a simple optical headend transceiver compatible with direct modulation or the more complex modes by using a PC to do the modulation and demodulation using DSP and SDR techniques.

My project is based on the eloquent technique of modifying a high power LED for both transmitting and receiving the light, as developed by Stuart G8CYW , allowing the use of only one set of optics such as a Fresnel lens or telescope system to be used instead of requiring a duplicate array for the receiver side with corresponding bulk, expense and tracking alignment of dual instruments.

Stuart's information describes modification to the readily available Osram Dragon series LED, whereby the internally mounted reverse voltage protection diode must be removed from the circuit. The 1W and 3W class red LEDs are encapsulated in a gel, so this operation is possible using a surgical blade to cut the gold wire, best accomplished in circuit so that an effective cut is confirmed.

The 1W Golden Dragon LEDs in rx mode operate best with around 38v reverse bias, this is adjusted whilst aiming at a modulated light source such as a CFL or incandescent lamp. Sensitivity and bandwidth is a compromise. 3W Platinum Dragon LEDs need around 80v reverse bias. When used for reception, stray capacitance must be kept to a minimum therefore the high - Z preamp is best constructed by direct wires connection (standard VHF practices) to the LED. I have mounted the preamp, transmit modulator and -ve bias power supply inverter modules around the edges of the heatsink. Shielded tx audio, rx audio, +12v power and +12v tx power cables connect from the headend to microphone & monitor or PC and +12v power source respectively. Switchover to transmit mode is achieved by powering up the +12v tx line.

In my application, a general purpose telescope featuring Maksutov-Cassegrain optics was chosen and my least favourite 10mm eyepiece attached to the headend. The telescope is returned to optical or video use by swapping out the eyepiece in the usual manner. One problem was encountered: when attempting to align the telescope using the "red dot finder", the LED light was not visible - due to the red filters used in the supplied finderscope. A gunsight was attached in place of the original finder.

Now to the second feature used by Stuart G8CYW and the UK teams; complex modulation and IF subcarrier techniques.
In the UK it appears commonplace to use ssb transmission from a portable radio such as the FT817 by constructing a transverter mixing the RF signal down to the upper audio range of 10 or 20 kHz.
I thought it may be easier to use a standard PC laptop running one of the SDR soundard programs,

http://www.g4jnt.com/SDRTxSW.htm
and

http://sourceforge.net/apps/mediawiki/drm/index.php?title=Main_Page
with

http://www.rarewares.org/aac-decoders.php


Whilst these programs are limited in the frequency range available, it provides a compatible signal without the necessity to build a special transverter / transceiver combination

Echoes Of Apollo

Echoes Of Apollo [EofA] is an Amateur Radio event remembering 40 years on of the space missions to the moon and a small team of us designed, assembled, tested and operated a temporary station to participate.

Amateurs, usually known by first name and callsign (ZL2TV for our station), will transmit as powerful beam as available from their earth station to the surface of the moon whence it becomes scattered in the reverse to be received back on earth approximately 2.5 seconds later. The art is known as EME, for Earth-Moon-Earth, or simply moonbounce.

In 2009, when the inaugural EofA project to activate as many large Apollo-era dishes for a day of Moon talk  was announced, I had good reason to be interested. My workplace had one remaining 30.5 metre, fully steerable antenna that had been replaced with a smaller model and the site decommissioned, a fate already dealt to five similar size dishes and countless 10-metre class TVRO setups around the country.

Permissions were obtained and I had 3 weeks to plan the technical aspects of making it work on the 1296MHz frequency. Planning included the possibility of involvement with Scouting groups etc. to fully participate in EofA and the other big dishes that would be active on this weekend event. This is a beam waveguide-fed Cassegrain dish and the feed comprises of a corrugated horn of 0.85m diameter. I constructed a dual probe, cylindrical feed with 90 degree hybrid coupler, whilst Steve ZL1TPH constructed a round septum feed. The plan was to try both and go with one that worked, as the exact size of the hole in the horn could not be determined till the day.

Then a problem occurred requiring the old dish for service and we had to sit that one out for a year. Constructed equipment was quarrantined and plans were kept till the day came, about 2 days prior of the 2010 EofA event, that word came "go for launch".

Again there was no opportunity to pre-test any systems. Harry ZL1BK arrived to help with the final installation and keep the moon in our sights for the duration. The moon was already up but, our Saturday being early for most other stations (12 hrs ahead of UTC), we weren’t in a hurry. Sun noise was checked and less than anticipated …. final calibration suggests 12db was received.  After connecting a Spectran monitor laptop to the audio, echoes were identified and then heard on the speaker, as tuning and tracking were established. Opportunity was taken to measure the sun -3dB beam width when slewing the elevation. This occurred at 0.6 degrees, suggesting 0.2 degrees beam width in the antenna, something I expected as a consequence of illuminating the sub reflector from the same area of horn aperture designed for 4GHz. In effect, we were lowering the gain by limiting the field of view on 23cm to that provided on 3.7GHz, spilling the rest of the beam out to cold sky and/or the walls of the beam waveguide system and its 4 periscope mirrors and tube.

As far as possible, in keeping with EofA, 1970s equipment was used ... a Microwave Modules Ltd. converter, an Icom IC202s modified with Quindar tones  The LNA and SSPA (amplifiers) were somewhat more modern Mini-Kits from Australia and a 60 watts output combined pair of Aprisa TX boards from 4RF New Zealand.

EofA 2010 included the Arecibo dish on the 144MHz frequency and activity seemed to have moved from the original theme of "talk via the moon" on 1296MHz, so the challenge was to upscale to a band we could talk via the moon, such as the 5760MHz European activity session the following weekend. A homebrew transverter as normally used for local terrestrial operating, Icom IC706 exciter (to accomodate the large doppler shifts) and modified feed launcher were fitted up to the corrugated horn and testing showed cw (morse) echoes were possible down to 50 milliwatts power. Tests were also carried out , ssb and FM, and to TED ZL2IP in Inglewood direct. Own echoes on ssb at the highest power of 275 watts returned an etheral clarity which was quite unexpected both to ourselves and participating stations.

This size dish is not optimal for EME and was a two - person operation keeping it on track while operating via the moon, an unforgettable experience especially for us EME rookies at 3am on a misty night! The VK3UM Australian EME software deserves special mention it provides a lot of pre-planning, necessary as the Moon waits for no-one. It was pleasing to be able to put the antenna, which I was involved in building and testing during 1984, through some new paces - or should I say frontiers, before it wanders into the twilight zone.

Moonbase Alpha team - Ralph ZL2TV, Steve ZL1TPH, Harry ZL1BK, Colin ZL1BTT 5 GHz Ranging station - Ted ZL2IP QSL Manager - John ZL4JY

Archive

Prologue

Bear with me as this blog emerges from the beginning, many moons ago, somewhat before the family got our first transistor radio, then television, 19" of glorious grayscale with twin speakers. 

As with many households of the era, before Sputnik, the centre of the sitting room was a radiogram (well, in winter it was also the fireplace), made by Philco it ran with valves, sported a record player deck and a large dial with many scales including one called "shortwave".

This was the seed, my portal to the rest of the world and beyond - so long as it could reach through the swirling and static of the aether. It initiated my journey from building a crystal set to relaying voices via the moon and listening to the faint rumblings of a supernova remnant star.


Central to this has always been a passion for wireless, something that can be with you at home and away, operating in every environment, delivering communication, news, music, pictures with neither barrier nor tether.

If it needs wires it ain't wireless